This relates generally to imaging sensors, and more particularly, to imaging sensors with pixels that include more than one photosensitive region.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Imagers (i.e., image sensors) may be formed from a two-dimensional array of image sensing pixels. Each pixel may include a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical charges. Conventional image pixel arrays include frontside illuminated image pixels or backside illuminated image pixels. Image pixels are fabricated on a semiconductor substrate using complementary metal-oxide-semiconductor (CMOS) technology or charge-coupled device (CCD) technology. The image sensors may include photodiodes and other operational circuitry such as transistors formed in a front surface of the substrate. A single image sensing pixel in the two-dimensional array of image sensing pixels includes a single photosensitive region, a color filter formed over the photosensitive region, and a single dome-shaped micro-lens formed over the color filter. Certain image sensing pixels may include two or more photosensitive regions.
When viewed as a whole, the array of color filters associated with the array of image sensing pixels in the image sensor is referred to as a color filter array. Many imagers use a Bayer color filter array in which vertically and horizontally adjacent color filters in the array are of different colors. The Bayer color filter array includes red, green, and blue color filters. Ideally, photosensitive regions associated with a pixel having a red color filter would only be exposed to light that has passed through a red color filter, photosensitive regions associated with a pixel having a green color filter would only be exposed to light that has passed through a green color filter, and photosensitive regions associated with a pixel having a blue color filter would only be exposed to light that has passed through a blue color filter.
In embodiments where multiple photosensitive regions are formed in a single image sensing pixel, there may be undesired optical cross-talk between photosensitive regions within a single image sensing pixel. In many imagers, the photosensitive regions of any single given image sensing pixel are associated with a single color (i.e., a single color filter is formed over the single given image sensing pixel). Additionally, there is often undesired optical cross-talk between adjacent image sensing pixels associated with different colors (i.e., image sensing pixels having color filters of different colors). Undesired optical cross-talk within a single given image sensing pixel is characterized by light passing through a portion of a color filter formed over a first photosensitive region in a single given image sensing pixel and impeding (and consequently generating charge) in a second photosensitive region in the single given image sensing pixel. Undesired optical cross-talk between pixels is characterized by light passing through a color filter of one color and impeding on a photosensitive region of a pixel associated with a different color. An example of undesired optical cross-talk is when light that has passed through a red color filter impedes on a photosensitive region associated with a green pixel (i.e., a pixel having a green color filter). Optical cross-talk (both between pixels and within a pixel having multiple photosensitive regions) is often caused by high incident angle light and flare conditions, and can degrade the output image quality of an imager.
It would therefore be desirable to be able to provide improved image pixels for imaging devices.